import java.util.Scanner;

public class Main1337 {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double L = sc.nextDouble();
        double pi=3.14;
        double r=L/2.0/pi;
        double S=pi*r*r ;
        System.out.println(String.format("%.2f",S));
        }
    }
